Field of the Invention
This invention relates to illumination and display fields, and in particular, it relates to a light emitting device and related light source system.
Description of Related Art
In conventional projection and display fields, a commonly used technique for providing a white light source is by using a blue excitation light to excite a yellow phosphor to generate a yellow light, and mixing the yellow light with unabsorbed blue light to generate a white light. In this technique, because 445 nm blue laser light has a relatively high excitation efficiency for the phosphors, 445 nm blue laser light is often used as the excitation light source. However, the color of the 445 nm blue light is slightly purple, and is not suitable for direct use in projection. Therefore, an improved technique uses a 455 nm blue light to excite the yellow phosphor to generate the yellow converted light, and uses a 462 nm blue laser to be mixed with the yellow converted light to generate the white light.
Refer to FIG. 1, which schematically illustrates the structure of a light source system according to a conventional technology. The light source system includes a first light emitting device 10, a second light emitting device 20, a wavelength conversion device 30 and a light collecting system 40. The first light emitting device 10 includes a first laser array 101 and condenser lens 102. The first laser array 101 includes multiple laser elements, for generating 455 nm blue laser light. The light generated by the first laser array 101 is collected by the condenser lens 102 and output. The second light emitting device 20 includes a second laser array 201 and condenser lens 202. The light generated by the second laser array 201 is collected by the condenser lens 202 and output.
The light collecting system 40 includes a filter plate 401 and a collecting lens 402, where the filter plate 401 transmits blue light and reflects yellow light. The light emitted by the first light emitting device 10 and the second light emitting device 20 are respectively incident on the filter plate 401 from its two sides, where the light emitted by the first light emitting device 10 sequentially passes through the filter plate 401 and the collecting lens 402 to reach the wavelength conversion device 30. The wavelength conversion device 30 includes a wavelength conversion layer, which includes a yellow phosphor, for absorbing the blue laser light from the first light emitting device 10 and generating a yellow converted light. The yellow converted light is collected by the collecting lens 402 and then incident on the filter plate 401; it is reflected by the filter plate 401, and combined with the light emitted by the second light emitting device 20 which is transmitted by the filter plate 401, to become an output light beam.
Because the laser light has a Gaussian distribution, while the converted light has a Lambertian distribution, to more uniformly mix the light emitted by the second light emitting device 20 and the yellow converted light, the second light emitting device 20 further includes a light homogenizing rod 203, disposed on the output light path of the condenser lens 202, to homogenize the blue laser light outputted from the condenser lens 202. Meanwhile, to make the light power density of the light spot formed by the first light emitting device 10 on the wavelength conversion device 30 more uniform, and to improve excitation efficiency, the first light emitting device 10 further includes a light homogenizing rod 103, disposed on the output light path of the condenser lens 102, to homogenize the blue laser light outputted from the condenser lens 102.
However, because such a light source system includes many optical elements, its size is large. One solution for this problem is to combine the first laser array and the second laser array into one laser array, and to use one condenser lens and one light homogenizing rod to collect and homogenize the light. However, in the downstream light path, if the 445 nm blue light and the 462 nm blue light are separated using wavelength-based light separation, because the wavelengths of the two blue lights are relatively close, the filter plate is required to have a very steep light filter curve, which increases cost.